1. Field of the Invention
This invention generally relates to access devices that provide working channels through a body wall and into a body cavity and, more particularly, to instrument seals in laparoscopic trocars.
2. Discussion of Related Art
Less invasive abdominal surgery, commonly referred to as laparoscopic surgery, is undertaken with instruments extending across the abdominal wall. With this procedure, the volume of the abdominal surgical site is increased by inflating the abdomen with gas. In order to maintain the pressure of the gas within the abdomen while passing instruments across the abdominal wall, access devices such as trocars, are positioned through holes in the abdomen. These trocars are provided with seals which engage the instruments as they are passed through the trocars and into the inflated abdomen. That is, in addition to providing a pathway for surgical instruments, the trocar is used to communicate a pressurized gas flow into an abdominal cavity so that the body cavity is expanded under a positive gas pressure.
The trocar, therefore, must have a combination of seal members that prevent gas from escaping the abdominal cavity. It is important that the gas pressure be maintained at a constant pressure and volume. Generally, the trocar comprises a cannula that traverses the abdominal wall and a seal housing that contains the requisite seals. Typically, a common seal arrangement comprises a first seal sized and configured to serve as a check valve when there is no instrument within the working channel of the trocar, and a second or septum seal sized and configured to seal around an inserted instrument.
The seals associated with the trocar are unique in that they must be very dependable, durable, unobtrusive and respond to a wide variety of instrument sizes and shapes. In particular, the seals should not interfere with or compromise the use of delicate surgical instruments, nor should the seals cause unwanted restriction or movement of an instrument. For example, an instrument must remain where it is placed. Furthermore, the seal must allow an instrument to move in, out and around the working channel and in a direction that remains as closely as possible to the wishes of the user. As such, there are many competing requirements in the construction of trocar seals.
In one example, a septum seal that is made of a very thin, resilient, durable material may have a tendency to leak as an instrument is moved from side to side within the working channel of the trocar. That is, the center opening or orifice of the septum seal may subsequently elongate as an instrument moves from side to side, causing a gas leak. To prevent this condition, the orifice of the septum seal may be reduced to a minimum. This arrangement, however, presents a problem when it is being used with a large instrument as it may draw the seal back into the orifice during withdrawal of the instrument from the trocar, causing the seal to invert and therefore binding between the instrument and orifice. This problem is addressed in Applicant's U.S. Pat. No. 5,584,850, which discloses an anti-inversion seal and which is incorporated herein by reference.
The anti-inversion seal of the '850 patent has proven to be effective in preventing the seal to invert and binding between an instrument and the orifice. Nevertheless, there remains a need in the art to improve the anti-inversion seals so as to make them more responsive to an increasing variety of instruments.